Question: I would like to know how gills work in fish?

Gills are very thin pieces of tissue through which fish’s blood flows. As tissue is quite thin, oxygen can diffuse across into the blood and waste products like carbon dioxide and ammonia can diffuse away (unless you haven’t cleaned the fish tank in a loooooong time)

We breathe air that contains oxygen in gas form, but for aquatic life the oxygen they require is in solution in the water. Gills have a huge surface area with lots of folds that allows the oxygen to diffuse from the water into the gills where it also has lots of blood vessels that pick up and allow the oxygen to flow around the fish’s body. Carbon dioxide from the blood goes the other way!

As we know all animals need oxygen to survive. Gills of a fish play a very similar to our lungs. Fish swallow the oxygenated water and moves it through their gills and then again out through the gill openings. It also pumps deoxygenated blood from the body into the gill ﬁlaments. As the oxygenated water passes near by the deoxygenated blood, oxygen moves from the region of relatively high concentration (in the water) to the area of lower concentration, in the blood. The efﬁciency oxygen transfer is increased by the blood and water ﬂowing in opposite directions; this is known as a mechanism. Using this counter-current exchange mechanism, a ﬁsh can actually extract up to 70% of the oxygen dissolved in the water. Isn’t that amazing?:)